Not applicable
One of the least expensive ways to move freight is by ship, and, indeed, cargo ships cross the oceans of the world hauling products from port to port, country to country. There are in particular container ships that carry cargo in large, uniform containers, such as standard, ISO 20-foot containers that meet the requirements of an international standards organization for size and configuration. The cargo containers are stacked on the large flat deck of a container ship and in its hold. Once in port, the containers are offloaded typically with an assortment of cargo handling cranes. Unloading these ships is, of course, a time-consuming task and requires a crew to assure that the right containers are removed safely and efficiently. Efficient loading and unloading are important in getting good utilization from a container ship and in meeting delivery schedules.
Once off-loaded from the ship, these containers may be loaded directly onto a truck frame with a set of wheels for hauling by tractor truck overland to a next destination. Alternatively, the cargo containers may be placed onto a smaller ship, called a lighter, for transport to a dock, a shallow water port or onto the beach in logistics-over-the-shore military operations.
Not every port or other commercial location has the large assortment of cargo handling cranes needed for off-loading large sea-going container ships. Present day fixed and mobile cranes or bridge cranes are often not practical because of cost, operating and maintenance constraints, and the time required to erect and deploy them. Furthermore, gantry cranes have relatively small workspaces within which they operate before the entire massive crane has to be moved down a permanent track on which vehicles and other objects may have inadvertently become obstacles. Even when the path is clear, the mobility limitation requires stopping the crane""s operation, stowing the boom and outriggers, moving, and redeploying the boom and outriggers before operations can resume. Large rail cranes are also physically limited. Current ship-carried systems can sometimes compensate for limited port facilities, but because of the large pedestal size needed to support a rotating crane that can cover the ship deck, this is generally achieved at the expense of considerable cargo space or by requiring a separate crane ship to load and unload a cargo ship. In no case can they operate outside of well-protected port facilities where sea state three or higher conditions occur most of the time.
Loading and unloading containers using overhead or gantry cranes, in addition to their limited range of motion, have another problem. These types of cranes have X-Y actuation mechanisms from which a cable hangs like a pendulum. The pendulous nature of the gantry crane makes it less suitable for certain purposes, namely unloading ships, because it is so difficult to have the carried payload follow a trajectory without swinging. The motion of the sea results in an additional instability that translates into large swings in the payload. High wind and foul weather even further impedexe2x80x94or stall altogetherxe2x80x94the process of loading and unloading these ships. When wind is blowing, the containers have to be restrained by crewmembers using ropes. This is a dangerous task. When the crane is on a ship and the sea is rough, the ship will roll and pitch, creating the same effect as high wind, namely, increased oscillation of the cargo container. Likewise, if the lifting mechanism is on a dock and the container is on the pitching, rolling deck of a ship, moving the container that is on the ship using the crane is a slow and difficult process. If the sea is too rough, such as sea state three or higher, unloading must be halted. Unfortunately, around the world, sea state three is common. There is a seventy percent chance that a ship will encounter sea state three or higher at any moment anywhere in the world.
In addition to their physical problems, traditional single boom shipboard crane systems are expensive, involve considerable maintenance, and require highly skilled operators. Dockside gantry cranes are also quite expensive to acquire, operate and maintain.
The field of robotics has developed rapidly over the past twenty years as electronic components that control robotic movements have gotten smaller and more robust. Robotic welding machines play a substantial role in manufacturing automobiles, for example. The concept of a robotic device is easy to grasp in general but hard to define with any specificity because of the large number of forms robotics devices may take. For example, robotic devices may be electrical, mechanical or electromechanical and may range from simple manipulators to vehicles for exploration of the surface of the moon, the planets or the ocean floor. Generally, however, the robotic device may be defined as a device that is capable of manipulating an object in a work place.
There is a particular type of robotic device, to which this patent lays claim, based on use of an array of cables attached to a lifting device. This xe2x80x9ccable array robotxe2x80x9d is defined as a robot that uses multiple cables connected together either directly or through an end-effector to manipulate an object in a workspace. A description of cable array robots is set forth by the inventor""s team in The Cable Array Robot: Theory and Experiment, by Gorman, Jablakow and Cannon, 2001, Proceedings of the IEEE International Conference on Robotics and Automation, incorporated herein in its entirety by reference.
Three-cable and four cable systems can be used to move loads within a workspace, and computers can be programmed to control this movement. Equations of motion for a multi-cable crane system, for example, are developed using Lagrange""s equations and certain assumed modes of operation. Then the resulting equations for four-cable arrays, which are kinematically redundant due to fewer degrees of freedom than the number of cables, are solved by first using a non-linear transformation to reduce the number of variables. An optimal-force distribution method can be applied to solve the transformed equations to yield a set of cable tensions needed to track a desired trajectory. The mathematical treatment of this subject is found in Optimal Force Distribution Applied to a Robotic Crane with Flexible Cables, by Shiang, Cannon, and Gorman, 2000, Proceedings of the IEEE Conference on Robotics and Automation, and Dynamic Analysis of the Cable Array Robotic Crane, by Shiang, Cannon and Gorman, 1999, Proceedings of the IEEE Conference on Robotics and Automation, both of which are incorporated herein in their entirety by reference.
The study of robotics may suggest the use of robots in the movement of cargo containers, but the complexities of real-world application, particularly in ship-to-ship movement of containers in sea state three conditions impose significant challenges. Nonetheless, there remains a need for a better way to move cargo containers than traditional cranes, particularly in loading and unloading ships during all weather conditions and in related tasks such as underway cargo replenishment, at-sea missile replenishment and mobile offshore basing. Other applications for the cable array robot cross a full range including hazardous waste remediation (e.g. radioactive waste drum handling in open fields), painting or de-icing vehicles (e.g. airplane servicing when they taxi into the workspace), open-pit mining (e.g. truck loading at the mine surface to avoid building and traveling miles of pit roads), and overhead pallet handling in manufacturing (e.g. to move pallets loaded with workpieces from one workcell to the next). The invention also envisions a new class of the world""s largest robots including array robots with workspaces of nearly unlimited size including construction sites between tall buildings and stockyards or port areas engulfing whole valleys or fjords between nearby mountains on which the system""s mast structures are mounted. Since there are many applications, for the cable array robot, the term end-effector hereinafter refers to any tool or sensor suite to which the cables of the cable array are attached, and the term container refers to any object with which such an end-effector may interact. In a navy sea basing application, for example, the end-effector may be a spreader and the container may be an ISO shipping container.
The present invention is a system and method for acting from overhead upon an environment such as when cargo is unloaded from a container ship onto a dock or other ship such as a lighter in shipping operations. The present invention has components in four basic categories: 1) the end-effectors (e.g. a spreader for gripping a standard cargo container in a shipping application, a pallet handler for gripping batches of workpieces in a manufacturing application or an excavating tool handler for using tools to expose and retrieve material in a hazardous waste remediation or open-pit mining application); 2) a multi-cable robotic array to move the end-effector throughout an extended workspace; 3) a computer controller with graphical user interface for allowing an operator to control the robotic array, and thereby the position and orientation of any objects such as a shipping container, that is attached to the end-effector; and 4) a system of cameras and sensors to provide information to the computer controller that is programmed to use the camera and sensor information as input to container movement decisions. Essentially, the operator uses this information in giving instructions (such as xe2x80x9cput that therexe2x80x9d directives to the programmed computer, which then controls the end-effector through supervisory control of the robotic array in moving a container. The computer interprets the operator""s instructions by ultimately translating operator directives into a set of tensions on the four cables of the robotic array throughout semi-autonomous trajectories. A supplemental power source and one or more offload fairleads are optional but useful additional components. Only the cables and cargo move, during operations, so the system is fast, stable, and energy-efficient as well as capable of covering a very large area compared to boom cranes that must slew with every move and even then can merely cover a limited work area.
The entire system of subsystems described herein was built at {fraction (1/16)}th scale (or xc2xc scale for some components) for a container offloading application at sea. Where more than one version of software and hardware was implemented, one implementation is referred to as the preferred embodiment. A videotape was made of the model in operation.
The robotic array may include folding, telescoping masts with winches and cables that cooperate to move the end-effector for the case where retractability of the masts is desired when the system is not in use. Each mast is seated in a supporting structure built into a platform, dock or ship deck. The tips of these masts, over which the cables pass, define the corners of the workspace. Cameras, located in one or more places (e.g. carried on the bridge of a ship or by the masts near the tip) provide a wide-angle field of view of this workspace.
The end-effector for handling ISO containers includes an active spreader and may include a messenger spreader. The end-effector grips and manipulates the container within the workspace using the features of the active and messenger spreaders. The messenger spreader may be deployed from the active spreader using four small winches on the latter, or using a pulley arrangement (a xe2x80x9cclothsline approachxe2x80x9d) that allows use of a main winch to lower the spreader, when a container must be retrieved from within the ship""s hold. The end-effector is capable of controlling the container""s roll and pitch attitude to compensate for the center of gravity of the container being off-center, and can rotate the container about a vertical axis. The end-effector also carries additional sensors and cameras for close-in views and control of the container and its own movements. Laser ranging is used, for example, to guide container landings and machine vision is used to guide container pick ups.
The computer controller is adapted to receive and process information and respond to directions from the operator. It is a real-time, automatic feedback computer programmed for high-level functionality so that the operator requires little computer skill and training and yet has considerable flexibility in choices of container movement. It is programmed with control algorithms and a point-and-direct graphical user interface that enables the operator to target any point in the work area. These algorithms solve, in real time, the closed-chain kinematics and dynamics equations for desired movement of the containers, and cause the computer controller to adjust the length of the cables from the mast assemblies by operating winches associated with each cable. The movement of the cables in turn moves the end-effector and its grasped container according to the solution found by the algorithms. The user interface is independent of the number of mast assemblies used as long as at least three are used.
The graphical user interface allows the operator to see an interwoven virtual/live workspace including both virtual and live objects. Virtual tools, as the team calls them, are selected from a toolbox of graphical representations of end-effectors that are available for a particular application. These virtual tools are overlaid on live images of the containers within that workspace. They are manipulated in the scene using a computer mouse or instrumented glove much like a real tool would be manipulated in a real scene. Both virtual tools and live objects appear on the same computer monitor, but the approach is not the same as telemanipulation. The virtual tool is moved freely with no corresponding robotic programming until the operator is satisfied that a particular position and orientation is correct for a desired pick point, place point or way point. Then a directive is given to the computer to store the point in an evolving robotic program. With two such virtual paintings (one to the object to be moved and one to the place to which the object is to be moved) in the live video scene the robot can be directed to xe2x80x9cput that there.xe2x80x9d The locations xe2x80x9cthatxe2x80x9d and xe2x80x9ctherexe2x80x9d have both position and orientation associated with them. The robot then automatically constructs trajectories to achieve the desired directive. In the container handling application, the operator selects a container to be moved simply by virtually touching the corresponding live video container shown on the monitor with the virtual tool (spreader tool in this case). The operator then designates, in a similar manner, the location where the container is to be moved issuing a directive to xe2x80x9cput that therexe2x80x9d. Finally, the operator has an option to see a trial run of the designated movement in order to verify that the movement can be safely made before the robotic array is activated to move the real container on the ship. During specification of a robotic task, especially in applications such as hazardous waste remediation, where tasks are very unstructured, the depth of the virtual tool in the live video scene is visualized relative to a triangulation point specified using one or more cameras with associated depth cue information (such as surface height relative to camera height). In this case, the virtual tools recede into partial wire frame rendering beyond the triangulation depth but return to fully rendered view in front of the triangulation point so that position and orientation relative to the container can be virtually specified in the live video scene. After directing the robot to xe2x80x9cput that therexe2x80x9d the computer simulation feature of the system presents the operator with a preview of how the container will be moved to the destination. Obstacles that may be hit during such a trajectory cause the screen to turn red, for example, as a warning so that the operator will know to move the obstacle (e.g. another container) before attempting the first move that was found to be dangerous. Upon operator approval of a virtual trajectory, the human computer interface automatically generates robotic commands to the hardware components to begin real-world trajectory execution.
The sensors cooperate using sensor fusion techniques to provide information regarding the location and relationship of objects on the ship, on the dock, and regarding the cargo container so that the proper container is selected and moved to the proper destination precisely and without undue oscillation. The sensors include cameras, global positioning satellite system sensors, laser range finders, encoders, tension sensors, and measurement sensors for sensing changes in the roll and pitch attitude of the container. These sensors monitor and control the cable array robot operations.
One feature of the present invention is the folding, telescoping masts. Because the tips of these masts define the upper and outer corners of the cargo movement workspace, their reach, being enhanced by their telescoping design, becomes important in the ability to move cargo. On the other hand, their ability to be folded into a compact configuration, reduces their impact on the maneuverability of the ship, such as, for example, when passing under bridges, being maneuvered into port, or weathering a storm at sea. Also, the present masts seat into prepared structural supports in the deck of a ship or on a dock, making them easy and quick to install and replace when necessary. The winches are generally located below deck and can be stored in standard containers when not in use.
The end-effector is another important feature of the present invention. It performs three functions. First it couples the container to the robotic array. Second it carries sensors that, when it is coupled to the container, allow the location, orientation and roll and pitch attitude of the container to be precisely controlled. Third, it is able to manipulate the container: rotating it about a vertical axis, damping oscillations and compensating for its roll and pitch attitude, in order to achieve control on the order of centimeters.
The cooperation of the end effector""s active spreader and its messenger spreader in retrieving containers from the hold is another feature of the present invention. This feature enables the robotic array to unload the hold and the deck without changes in equipment or set up time.
The graphical user interface is yet another important feature of the present invention. It is extremely easy to use, requiring little more than pointing and xe2x80x9cclicking,xe2x80x9d while issuing directives regarding what to perform at the indicated locations. Operators can learn to use it in minutes and will achieve 30-45 container movements per hour in Sea State Three (60-90 with a double array) compared to 10 containers per hour with the present crane-based systems, which can only operate in calm seas. Furthermore, the virtual reality aspect allows a test run of each movement prior to the actual movement as a safety precaution.
The use of cameras to provide images for object recognition and positional information for object location is another important feature of the present invention. By panning and tilting the camera to align an object with the camera""s cross hairs, the camera can locate an object. Using multiple cameras to triangulate on an object provides accurate positional information about an object prior to movement.
The use of sensors on the end-effector to assure that it is in position to lock onto a container and verify its position with respect to the deck is still another feature of the present invention and helps to assure that the container is securely coupled to the end-effector prior to movement. Sensors on the end-effector also allow roll and pitch attitude to be controlled, allow prevention of pendulation of the container below the spreader (from the points of cable attachment) and help to level the container when its center of gravity is not at the geometrical center of the container.
Using the differential global position satellite (DGPS) system to provide constant feedback as to where the end-effector is during movement is important, particularly when the container and the surface for which it is destined are moving with respect to each other, such as when the container is being moved on rough seas from a ship to a lighter not tethered to the ship. DGPS system provides a basic frame of reference for the movement.
Still another advantage of the four mast assemblies of the present invention is its operational flexibility. Not only can the four-mast system load and unload a cargo ship from a dock or sea-going lighter, but it can also load another ship. This can either be accomplished by overhanging the other ship, or two masts of a four-mast system can cooperate with one or more masts on the second ship to pass cargo containers between ships.
A significant advantage of the present system is that it avoids the need for large cranes, forklifts, and miscellaneous material handling equipment and support personnel. Moreover, the components of the present system can be prefabricated and transported in ISO containers themselves. Finally, the computer controller for the present system can also be used for logistics, materials inventory, operating, and accounting functions.
The present system allows readjustment of containers while a container ship is underway, for example, to prioritize the cargo for offloading operations or increasing stability of the cargo loadxe2x80x94another significant advantage. In essence, the invention provides horizontal and rotational control authority for the first time in crane technology. This means there will be no pendulation (swing) and no undesired yaw motion (swivel) during container movementsxe2x80x94despite ship roll, heave and pitch.
Many other features and their advantages will be apparent to those skilled in the art of cargo handling and robotics from a careful reading of the Detailed Description of Preferred Embodiments, accompanied by the following Drawings.